enhance(backend): Improve behavior of correctFilename (#11484)

* enhance(backend): Improve behavior of correctFilename

* ✌️

* 未知のファイル形式かつ拡張子がある場合は何もしない

* ✌️

* .ext

---------

Co-authored-by: syuilo <Syuilotan@yahoo.co.jp>

packages/backend/test/unit/misc/correct-filename.ts

@@ -0,0 +1,48 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and other misskey contributors
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { correctFilename } from '@/misc/correct-filename.js';
+
+describe(correctFilename, () => {
+    it('no ext to null', () => {
+        expect(correctFilename('test', null)).toBe('test.unknown');
+    });
+    it('no ext to jpg', () => {
+        expect(correctFilename('test', 'jpg')).toBe('test.jpg');
+    });
+    it('jpg to webp', () => {
+        expect(correctFilename('test.jpg', 'webp')).toBe('test.jpg.webp');
+    });
+    it('jpg to .webp', () => {
+        expect(correctFilename('test.jpg', '.webp')).toBe('test.jpg.webp');
+    });
+    it('jpeg to jpg', () => {
+        expect(correctFilename('test.jpeg', 'jpg')).toBe('test.jpeg');
+    });
+    it('JPEG to jpg', () => {
+        expect(correctFilename('test.JPEG', 'jpg')).toBe('test.JPEG');
+    });
+    it('jpg to jpg', () => {
+        expect(correctFilename('test.jpg', 'jpg')).toBe('test.jpg');
+    });
+    it('JPG to jpg', () => {
+        expect(correctFilename('test.JPG', 'jpg')).toBe('test.JPG');
+    });
+    it('tiff to tif', () => {
+        expect(correctFilename('test.tiff', 'tif')).toBe('test.tiff');
+    });
+    it('skip gz', () => {
+        expect(correctFilename('test.unitypackage', 'gz')).toBe('test.unitypackage');
+    });
+    it('skip text file', () => {
+        expect(correctFilename('test.txt', null)).toBe('test.txt');
+    });
+    it('unknown', () => {
+        expect(correctFilename('test.hoge', null)).toBe('test.hoge');
+    });
+	test('non ascii with space', () => {
+		expect(correctFilename('ファイル 名前', 'jpg')).toBe('ファイル 名前.jpg');
+	});
+});